1. Technical Field
The present invention relates to a method for manufacturing a printed circuit board, and particularly to a method for manufacturing a multilayer printed circuit board having different flexibility in different areas.
2. Discussion of Related Art
Flexible printed circuit boards (FPCB) have been widely used in electronic products such as mobile phones, printing heads and hard disks. In these electronic products, some parts may move relative to a main body. In such condition, FPCBs are applied to provide electrical connections and signal transmissions between such parts and the main body due to their excellent flexibility. However, in some complex applications, there is a desire to provide a printed circuit board that is flexible in one end and is relative rigid in another end.
FIG. 1 shows a multilayer PCB structure 100, which has a first PCB substrate 110 and a second PCB substrate 120 having different length thereby forming a thick area 101 and a thin area 102 within the same PCB structure 100. The first and second PCB substrate 110, 120 are both flexible PCB substrate. It is to be understood that the thick area 101 has a higher circuit density, whilst the thin area 102 exhibits higher flexibility. To further increase a rigidity of the thick area 101, the PCB substrate 110 can also be a rigid PCB substrate.
Referring to FIGS. 2-5, during a manufacturing process of the PCB structure 100, firstly, a first PCB substrate 110, a second PCB substrate 120, and an adhesive layer 130 having a preformed opening 131 formed therein are laminated. As shown in FIG. 3, when a high pressure is applied on the first PCB substrate 110, the first PCB substrate 110 bends at the opening 131 and produces a concave portion 141 in an outer surface of the first PCB substrate 110. As shown in FIGS. 4 and 5, the concave portion 141 may cause a series of problems in sequential exposing, developing and etching step. For example, the obtained conductive traces 143 may have non-uniform line width or over etched. A stability of the obtained PCB deteriorates greatly.
Therefore, there is a desire to provide a method for manufacturing a multilayer printed circuit board having different thicknesses in different areas without decreasing quality of the printed circuit board.